This invention relates to apparatus for measuring flow parameters of a fluid such as flow rate and direction, and more particularly to improved transducer apparatus for this purpose.
Many different types of transducers are known for measuring flow parameters. Examples of known transducers include hot-wire anemoneter resistive-type devices, rotary cup devices, axial flow propeller rotary devices, and pressure-sensing devices which rely upon the deflection of a diaphragm or some other member to measure flow rate. Also known are electrofluid magnetic, optical, and sonic doppler-type devices. Known flow transducer devices have a number of disadvantages. Many are non-directional, being unable to discriminate between differences in flow direction, or have poor directional resolution. Many are bulky and have poor spatial or temporal resolution, and additionally cause perturbations in the flow medium being measured which lead to inaccuracies in the measurements. Some devices are expensive or require complicated processing, and many are unsuited for use in hostile environments. Many known devices also do not have sufficient sensitivity to measure very small changes in flow parameters, or are subject to error due to the effects of gravity or to the static pressure of the flow medium in which they are employed.
In some applications, such as investigating fluid flow through a channel or across an airfoil, it is necessary to develop flow gradients. This requires measuring the flow rate and direction at a plurality of points. The transducers employed for measuring the fluid flow must have good spatial, directional, and temporal resolution, and good sensitivity. Furthermore, the perturbations induced in the flowing fluid by the presence of the transducers must be minimized, and the calibration of the transducers themselves must remain unaffected by changes in their positions or the static pressure of the flowing fluid. U.S. Pat. No. 3,964,306 to Fletcher et al discloses a moving magnetic armature electromagnetic flow transducer, based upon a stereophonic phonograph cartridge, which employs a spherical probe. Although this transducer has good spatial resolution and is capable of measuring the components of flow velocity in two dimensions, it has a rather bulky structure which disturbs the fluid flow in the vicinity of the probe, and it suffers from other disadvantages.
It is desirable to provide transducer apparatus for measuring flow parameters of a fluid which avoids the foregoing and other disadvantages of known transducer apparatus, and it is to this end that the present invention is directed.